FAKE.Deploy WorkDirectory fix #461

When you install `Fake.Deploy` as Windows service your `CurrentDirectory` will be `C:\Windows\system32`. So if you have relative path in `WorkDirectory` variable, `IO.Path.GetFullPath` returns path relative from `C:\Windows\system32` what is not intuitive.

I am sure that `Fake.Deploy` should operateы identically in both modes (console & windows service).